In a large number of applications, structures are assembled or clamped together with fasteners, or tightened together to prevent fluids leaking from between the structures. This requires proper torquing with compressive loads being applied to fasten the structures together. Thus, torquing is a means by which users, assemblers, or mechanics tighten a fastener to a designed or desirable tension to thereby impart a compressive force against two structures such as an engine cover and an engine block. Torquing also creates friction on the threads of a threaded fastener, which serves to prevent the fastener from unintentionally unscrewing due to vibration.
The force applied to the fastener to preload the fastener is usually expressed in foot-pound units. Generally speaking, the torquing process involves determining a desired torque value for a particular application, and then, with a torque wrench or by other means, the head of the bolt, or a nut threaded onto the bolt, is tightened until the desired torque value is achieved. Torquing is also performed on some large bolts by stretching the bolt with hydraulic or other devices, screwing a nut on the bolt as far as possible, and then removing the stretching force. Yet another way to tighten certain bolts is to heat the bolt until it expands sufficiently, then screw a nut on the bolt as far as possible, and then let the bolt cool and shrink in length. The load applied by the bolt transfers across the structures being fastened together by the bolt, thereby creating a compressive force in the structures.
In large manufacturing plants, such as an automotive plant, where torquing is required for a large number of bolts, the torquing process itself can be time consuming and expensive. This is because, among other things, each individual bolt requires individual attention to ensure that it is tightened to the proper torque.
In addition to the time, labor, and costs involved in torquing large quantities of bolts, maintenance of torque wrenches and torque machines used to tighten the bolts results in further expenses. For example, torque wrenches and torque machines have moving parts which can break, and the torque devices require routine service and calibration to maintain them in good working order. Large bolts, such as those employed in the oil exploration/production, present safety concerns due to their size and weight. Bolts used on oil platforms can be up to approximately one foot in diameter. Thus, to torque such large bolts to the desired torque value, a mechanic must use correspondingly large tools which can cause severe injuries if mishandled. Furthermore, bolts used for construction in challenging environments such as underwater or in space are difficult to torque by any means.
Accordingly, there is a need for a self-torquing fastener that torques itself to a desirable value with minimum human intervention. The use of self-torquing fasteners minimize the time, cost, and will improve the safety involved in the torquing operation.
The present invention provides a new and unique self-torquing bolt and methods for torquing a first structure to a second structure. Preferred embodiments include a bolt that changes from a first shape to a second shape with the application of heat, and remains in that second shape even after the bolt cools.
In one embodiment, the aforementioned bolt is configured with a cavity, wherein the cavity is configured to store chemicals which, when reacted, emit heat sufficient to change the bolt from the first shape to the second shape.
In another embodiment, a two-part bolt assembly comprising an inner bolt and an outer threaded collar made from a shape memory alloy is provided. The inner bolt further includes a threadless stem and an axial retainer, and the threaded collar further includes a channel and an annular space. The bolt is disposed within the annular space and is attached to the threaded collar by the axial retainer.
These as well as other objects and advantages of the present invention will be apparent from the following specification and the accompanying drawings, which are for purposes of illustration only. Furthermore, it is understood that the changes in the specific structure shown and described may be made within the scope of the claims without departing from the spirit and scope of the invention.